HADOOP-12567. NPE in SaslRpcServer. Contributed by Sergey Shelukhin.

(cherry picked from commit 7fab5c8cec)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -705,6 +705,8 @@ Release 2.8.0 - UNRELEASED
     HADOOP-12560: Fix sprintf warnings in {{DomainSocket.c}} introduced by
     HADOOP-12344 (Mingliang Liu via Colin P. McCabe)
 
+    HADOOP-12567: NPE in SaslRpcServer (Sergey Shelukhin via cnauroth)
+
   OPTIMIZATIONS
 
     HADOOP-12051. ProtobufRpcEngine.invoke() should use Exception.toString()

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/SaslRpcServer.java

@@ -322,8 +322,9 @@ public void handle(Callback[] callbacks) throws InvalidToken,
         }
         if (ac.isAuthorized()) {
           if (LOG.isDebugEnabled()) {
-            String username =
-              getIdentifier(authzid, secretManager).getUser().getUserName();
+            UserGroupInformation logUser =
+              getIdentifier(authzid, secretManager).getUser();
+            String username = logUser == null ? null : logUser.getUserName();
             LOG.debug("SASL server DIGEST-MD5 callback: setting "
                 + "canonicalized client ID: " + username);
           }